212 TWENTIETH REPORT ON THE STATE CABINET. 



depressions ; the lower side, for little more than half the height, being the 

 sub-oval cell-aperture ; while the upper part is the semi-oval flattened area 

 at the base of the next succeeding cellule, as shown in fig. 11, Plate ii. 

 In this case the cellules are shown to be separate and distinct tubes, closely 

 pressed against the lateral walls of the stipe on one side, and communica- 

 ting with the common body by a slightly narrowed passage, as shown in 

 figure 12, Plate ii, which represents a longitudinal section of the body. 

 In a transverse direction, the base of the cellule is wider than the aperture 

 (fig. 11, PL iii). 



Specimens of this character, on becoming flattened, would present a form 

 where the cellules, though inclined against the common body, would not 

 overlap each other, and where the margin of the cellule is directed 

 backward instead of forward. Were these cellules to be prolonged, they 

 would overlap the next in advance, presenting in this condition but a slight 

 modification of the usual forms of Diplograptus. These deviations from 

 typical forms are so slight as to offer no sufficient ground for generic 

 separation. 



There are, however, a few examples, where the stipe is marked by a 

 range of cellules upon each side of the central axis, which appear to be 

 properly separated from Diplograptus, on account of the form and structure 

 of the cellules. These are apparently quite unlike those of G. pristis, and 

 others of that sub-genus, The Graptolithus bicornis, and two or three 

 allied forms, when flattened in the shale, show, as already described, a 

 simple semi-elliptical notch in the margin of the stipe, nearly rectangular 

 to the axis. This is well shown in fig. 3, Plate vi, of M. Barrande's 

 memoir, and also in Mr. Salter's illustrations of Graptolithus teretiusculus 

 of HisiNGER.* It is represented, less perfectly, in the figures of Prof. 

 Harkness,! and in most of my own figures on Plate Ixxiii of the first 

 volume of the Palaeontology of New- York. When compressed rectangularly 

 to the cellules, the apertures are transversely oblong-oval ; and the same 

 form is shown when looking upon the celluliferous margin of an uncom- 

 pressed stipe. 



The structure of these stipes and their cellules has already been 

 described in a preceding section, with reference to the figures illustrating 

 the same. The G. bicornis, known in New- York and Canada, may be 

 considered the type of a group of species of which we have two in the 

 shales of Norman's Kill near Albany, one in Ohio, and a similar or identi- 

 cal form in the Utica slate at Collingwood in Canada West. I would 

 include in the same group figs. 6 and 6 of Plate iii, as well as figs. 7, 8 

 and gl5, Plate ii of M. Barrande's Memoir, Graptolithus teretiusculus 

 of HisiNGER, and those referred to the same species by Salter. 1^ The 



* Quarterly Journal of the Geol. Society of London, Vol. viii, pi. xxi, figs. 3 and 4. 



t Id. Ibid., Vol. vii, pi. i, fig. 11. 



X Quarterly Journal of the Geological Society, Vol. viii, pi. xxi. 



